Over the years there have been many attempts to construct a sole unit for an athletic shoe to meet varying requirements of feel, function and support as well as to construct a sole unit of varying materials. To this end, for example, there have been attempts to provide a sole unit with better memory characteristics and an increased capability of dispersion of shock during running, as well as to meet other demands of various running groups. U.S. Pat. Nos. 2,563,438 (Weidner), 4,302,892 (Adamik), 4,316,335 (Giese et al), 4,364,188 (Turner et al), 4,364,189 (Bates) and 4,506,462 (Cavanagh) and 4,551,930 (Graham et al) would appear to be representative in their disclosures of these prior art attempts.
Turning to the prior art, the Weidner patent discloses a construction of sole including an outsole formed preferably of leather and a strip which circumscribes the outsole. The strip is formed of rubber or similar material. The outsole may be bonded to the outer surface of an insole, and the strip may be bonded around the outsole to the marginal edge of the upper. It is indicated by the patentee that the strip which lies in the plane of the outsole assists in the provision of a cushioned walk.
The Adamik patent discloses an intermediate sole which has some similarity to the outsole and strip disclosed by Weidner. The intermediate sole includes a core and an outer portion located along the entire outer periphery of the intermediate sole. The core and the outer portion along the outer periphery are both fabricated from a closed cell foam, and the hardness of the closed cell foam forming the core is less than the hardness of the closed cell foam forming the outer portion.
The Giese et al patent discloses a construction of intermediate sole that generally follows the construction of both Weidner and Adamik. To this end, the intermediate sole includes an outer portion and a core portion. Again, the outer portion is an outer peripheral portion.
The Turner et al patent discloses a running shoe of a construction similar to the construction of the athletic shoe described by Giese et al. According to Turner et al, the midsole includes a pair of resilient inserts, one within a recess in the area of the heel and the other within a recess in the area of the forefoot of the sole. The inserts may be formed of a foamed, closed cell material having a hardness substantially lower than the hardness of the midsole to provide a cushioning effect. In addition, Turner et al disclose that a plurality of plugs formed of hard rubber and having a hardness greater than the hardness of the midsole may be located in a region toward the medial side of the midsole, between the edge and the heel insert. The plugs provide heel stabilization by increasing resistance to compression at the medial side of the heel portion of the midsole. Turner et al disclose further forms of heel stabilization provided by triangular prism shaped portions, and by a mass of resilient material secured within a notch. The notch and prism shaped portions are located along the medial side of the heel.
The Bates patent discloses a running shoe having differential cushioning characteristics. To this end, Bates discloses a midsole having different measures of firmness along the medial and lateral sides. According to Bates, the material along the medial side of the midsole has a firmness approximately twice that of the firmness of the material along the lateral side of the midsole.
The Cavanagh patent discloses a midsole and a heel sole layer which supports the midsole. The heel sole layer, further, is formed by two portions which extend longitudinally along the medial and lateral sides, respectively, of the heel sole layer. The portion along the lateral side of the heel sole layer may be formed of a synthetic foam material and the extending portion along the medial side of the heel sole layer may be formed of a material harder than the material along the lateral side.
The Graham et al patent discloses various components of a sole including an integral midsole/wedge, a midsole and a wedge which include a core of a first plastic material and a shell of a second plastic material substantially encapsulating the core. The different plastic materials impart different characteristics to the sole components.
While the athletic shoes which previously have been described may provide many desired and sought-after results, the sole unit, and particularly the midsole/wedge component of the sole unit adapted for use with footwear, such as an athletic shoe is considered to be an improvement over the known prior art.